Protective sheet material



Sept. 5, 1 944. KEMP 2,357,662

PROTECTIVE SHEET MATERIAL Filed June 12, 1941 INVENTOR Patented Sept. 5,1944 PROTECTIVE SHEET MATERIAL Milton 1i. Kemp, oak Park, n1., assignorto The Kendall Company, Boston, Mass., a corporation of MassachusettsApplication June 12, 1941, Serial No.' 397,733

6 Claims.

This invention relates to protective sheet material and moreparticularly to protective paper sheet c'overings for polished metallicsurfaces.

' Sheet metal is often supplied on the market with a finished surface.In a common form, the product is sheet steel provided with a platedmetallic surface and in many instances the metallic surface is given ahigh .polish and the sheet material is then shipped and stored in sheetform pending manufacture of stampings therefrom.

Manufacturers of these products as well as users find it highlydesirable to protect these polished surfaces after finishing andthroughout transportation and storage, and the most advantageous type ofprotection is afforded by a cheap protective sheet material as of paper,bearing some sort of an adhesive coating which has a pressureadhesiveness to the finished surface so that it can be easily aflixedover the surface. In some cases the sheet remains as a protectivecovering until subsequent cutting, stamping and even assemblingoperations have been completed.

Pressure sensitive adhesives of the type presently known have not beenfound wholly satisfactory by sheet metal manufacturers for theseprotective purposes, because, after continued contact with polishedmetal surfaces, these adhesives cannot be freely and readily removedfrom the metal, but leave considerable residues so firmly adherent as torequire resort to some liquid or expensive solvent treatment to removethe residues. Such residues are caused by adhesive breakdown ordecomposition resulting in adhesive delamination, and are due primarilyto poor aging quality brought on by contact of the adhesive with metalwhich attacks the adhesive.

Furthermore, the usual known types of pressuresensitive adhesives adheremuch too firmly to metal surfaces and are, therefore, not readilyremovable. Especially is this true when the adhesive is submitted toconsiderable pressure as it is when protected sheets of metal arestacked during shipment or storage.

Again, polished metal surfaces are susceptible to ready discolorationand staining, and it has been found that the staining and discolorationresulting from the use of usual pressure-sensitive adhesives is soserious as to amount to a commercially prohibitive number of rejects,which are so marred as to require complete refinishing.

It is therefore an object of this invention to provide a protectivesheet material which, when used in manners required by sheet metalmanufacturers for protecting metal surfaces, either polished or dull,will not adhere too firmly to the surface, will not break down or becomemushy during storage, and will not leave adhesive residue when removedor otherwise mar the metallic;

surface, despite all normal pressures which may be encountered duringshipment and despite contact therewithover long periods of time.

With these objects in mind, I have discovered that many compoundsheretofore generally used in formulating pressure-aggressive orpressuresensitive adhesives for securing proper tack and adequate agingqualities are advantageously discarded in preparing an adhesive for usewith a backing as a protective sheet for metallic surfaces found onsheet materials of the type which have been described. Thus certainwaxes, certain accelerators, certain anti-oxidants, and some of the Wellknown types of plasticizers have been found to have deleterious effects.Waxes especially bloom to the surface and cause undesirable residualdeposits, etching or staining.

Limitation as to acceptable ingredients has therefore created particularproblems in securing an adhesive of proper tack and with good agingqualities to secure suitable adhesion without breakdown orresidue andwhile preserving the non-staining characteristics found essential.Attempts to include certain ingredients, as antioxidants, to lessen thebreakdown and secure better aging qualities usually produce unsuitablemetal-staining or metal-discoloring adhesives.

I have found that natural rubber may be retained as a major ingredientin the adhesive mass for the purposes of this invention, provided thatthere is.included as a protective agent for the rubber, a quantity ofthe synthetic material permits the omission of ordinaryage-resistanceproducing and tack-reducing agents, which I have found tobe unsuitable for metal because of their metal staining or discoloringproperties. Thus, a highly satisfactory protective sheet material may beformed by coating asheet backing such as paper with an adhesivecomprising a mixture of pale crepe rubber and Perbunan (a mixedpolymerizate comprising a mixed or copolymer of butadiene and acrylicacid nitrile). Preferably the adhesive is prepared in accordance withthe following formula:

Pale crepe rubber 200-800 Perbun'an -l This compound may be formulatedon a rubber mill, and can be calendered in known manners onto a paperbacking. or it may be solvent spread.

Parts by weight I 2 4 asuaeca In general, the less the proportion ofPerbunan to rubber the more sticky or tacky the mass will be. I-havefound that an adhesive prepared in accordance with the above formula hasthe correct properties of tack and adhesion for use on po1- ished ordull metallic surfaces such. as nickel plate, chromium plate, copper orbrass. thaprotective ma rial is applied to surfaces of null r polishednickel or polished chromium,

stable adhesive resistant to breakdown by metal attack and havingslightly tacky qualities rendering the sheet material pressure-adherentto smooth metallic surfaces, said adhesive being and subjected to thevery exacting test of 48 such a test may be removed from the surface fby a stripping action without leaving a deposited adhesive residue,indicating high coherency and non-delaminating qualities, even afterprolonged metallic contact. Even when applied to copper and brass, thisadhesive is not decomposed under the same test, and the results oncopper and brass, as well as on polished zinc, are, so far as breakdownand grab are concerned, equally successful and, as to residue, are amarked improvement, even in the absence of inhibitors, over previouslyknown adhesives, especially inasmuch as any minute residues may beeasily wiped off without liquid or solvent treatment such as previouslyrequired. Inall of the above applications, no detrimental staining oretching of the polished or otherwise finished surfaces'is encountered.

The accompanying drawing illustrates a roll of protective material andits application as a protective sheet on a sheet of metal 8, as ofsteel, bearing a plated polished metallic surface II. The protectivesheet comprises, as shown, an intermediate flexible backing material H,as of paper, bearing on its under-surface the pressuresensitive adhesiveof this invention ll. The protective sheet shown also bears a backcoating IQ of a repellent material in accordance with well knownpractice which requires no further description. The use of such arepellent coating l6 aids in the unrolling of the materials from theroll i8 without undue adhesion of the pressuresensitive surface It tothe roll.

As will be understood, the thickness of certain of the materials isexaggerated in the drawing for purposes of clarity, and the roll, thesheet material and the plate are broken away along their far edges.

While in its preferred use as a protective coating on finished sheetmetal, the adhesive will very likely not encounter high temperatures,the adhesive of this invention does have high heat resistant qualitieswhich would favor its use for protective purposes where elevatedtemperatures are required, for instance in masking metal or othersurfaces duringa iapanning operation.

By and large, the adhesive of this invention is not considered as whollysatisfactory for use on resinous surfaces such as lacquered brass orcopper, though, for some uses, it might prove entirely adequate and adecided improvement over protective tapes now ofiered.

Iclaim:

l. A protective sheetimaterial for smooth pol-- ished metallic surfaces,comprising a flexible sheet backing having on one surface thereof aformed of milled rubber from about 66 to 89% and, as the predominantremaining ingredient, a mixed polymerizate including polymerizedbutadiene, said adhesive being substantially free of metal-stainingwaxes and metal-staining antioxidants.

. 2. A protective sheet material for smooth polished metallic surfacescomprising a flexible sheet backing having firmly-adherent to one sidethereof a coating of a slightlyv tacky stable adhesive resistant tobreakdown by metal attack and including as essential ingredients a majorproportion of rubber and a minor proportion of a protective agent forsaid rubber consisting of a mixed polymerizate including polymerizedbutadiene, said adhesive being substantially free of metal-stainingwaxes and metal-staining antioxidants.

3. A protective sheet material for. smooth polished metallic surfacescomprising a thin flexible sheet backing having firmly adherent to oneside thereof a coating of a slightly tacky stable adhesive resistant tobreakdown by metal attack and formed of from about 66 to about 89%rubber and, as the predominant remaining ingredient, a butadiene-acrylicacid nitrile mixed polymerizate, said adhesive being substantially freeof metal-staining waxes and metal-staining antioxidants.

4. A protective sheet material for smooth polished metallic surfacescomprising a flexible sheet backing having firmly adherent to one sidethereof a coating of a slightly tacky adhesive resistant to breakdown bymetal attack and consisting essentially of a milled mixture of a majorproportion of rubber and a minor proportion of a butadiene-acrylicnitrile mixed polymerizate, said adhesive being substantially free ofmetal-staining waxes and metal-staining anti-oxidants.

5. A pressure-sensitive adhesive comprising a slightly tacky massresistant to breakdown by metal attack containing rubber from about 66to 89% and an age-resisting protective agent for the rubber constitutingthe only other ingredient of the mass, said protective agent consistingof a mixed polymerizate including polymerized butadiene.

6. A protective sheet material for smooth polished metallic surfaces,comprising a thin flexible sheet'backing having on one surface thereof athin exposed coating of an age-resisting, nondelaminating adhesivehaving slightly tacky qualities rendering the sheet materialpressure-adherent to smooth metallic surfaces and consisting essentiallyof rubber and of a butadieneacrylic acid nitrile mixed polymerizate as aprov tective-agent for said rubber in the proportions by weight of'aboutone part of protective agent to two to eight parts of rubber, saidadhesive being substantially free or metal-staining waxes andmetal-staining anti-oxidants and resistant to breakdown by metal attack,and said sheet material being readily removable from a smooth metalllicsurface after prolonged contact of said adhesive coating therewithwithout deposit of adhesive residue on said metallic surface.

MILTON H. KEMP.

CERTIFICATE OF CORRECTION Patent No. 2,557,662. I I September 5, 19M.

- MILTONfH. KEMP. I

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 2,second column, line 5, claim 1, before "89%" insert -about--; and thatthe said Letters Patent should be read with this correction therein thatthe same may conform to the record of the case in the Patent Office.Signed and sealed this 21pm day of October, A. "D. 19th.

' Leslie Frazer (Seal) Acting vCommissioner of Patents.

